Personal identification systems may be based on something someone has, such as a card or badge, something that someone knows, such as a PIN, or some characteristic of the individual, such as his fingerprints or speech pattern. Security for such systems is enhanced by utilizing two or more of the above in performing the identification.
For example, parent U.S. Pat. No. 4,720,860, discloses a personal identification system wherein the individual has a card or other small, portable device which contains a microprocessor programmed to utilize a secret algorithm to generate a nonpredictable number from a stored value unique to the individual and a time varying value provided for example by a clock. The nonpredictable value is preferably displayed on the device. The individual then enters his secret PIN into a central verification system, either directly or over a telephone line, causing the central system to access stored information corresponding to the individual and to utilize at least some of this information to generate a nonpredictable value at the central computer utilizing the same algorithm as at the individual's microprocessor. At the same time this is being done, the individual is entering the number appearing at that period of time on the display of his device. The two values will match, signifying identification of the individual, only if the individual has entered the correct PIN and if the individual has the proper device so that the nonpredictable code displayed corresponds to that being generated at the central verification computer.
In other systems, such as those shown in U.S. Pat. No. 4,599,489 issued July 8, 1986, the PIN may either be stored in the user's device, or may be entered by the user. If the PIN is stored in the device, it is read from the device by a suitable reader and causes the central verification computer to generate a unique challenge code to the individual. This challenge code may either be entered by the individual into his machine, or may be automatically sensed by the machine, and is operated on by the user's device to generate a unique nonpredictable code which is then entered into the central computer to effect verification.
One potential difficulty with either of the systems indicated above is that an unauthorized individual may be able to obtain access to the user's PIN by electronic eavesdropping, reducing the security provided by the system. If, for example, the PIN is transmitted over public lines, such as telephone lines, from the user to the central verification computer, it may be possible to tap these lines and intercept the PIN as it is being transmitted. If the PIN is stored in the device, someone obtaining the device surreptitiously may, through sophisticated means, be able to determine the PIN stored in the device and thus defeat the security of the system. Furthermore, any storing of a PIN or password in the portable device for comparison defeats the purpose of an independent identification factor and reduces security to a "thing" possessed.
A need therefore exists for an improved means of communicating a PIN or other user identification code to a central verification system such that someone tapping the line over which the code is being sent will be unable to determine the secret identification number and someone obtaining possession of the user device will also not be able to obtain access to the user's secret identification number from the device.